This invention relates to the formation of discrete lengths of thermoplastic material in solidified form generally known as pellets. Such pellets are most often formed by the conventional melt extrusion of material through a series of passages. The thus formed strands are cooled as they emerge from the die and cut into individual lengths. Such pellets are utilized as free flowing molding granules for a number of processes such as injection molding and the like.
In order to realize pellet production of consistent size and shape without common occurrences such as fines, smears, and the like, it is normally necessary to utilize rotating knife structures mounted at the face of the die. Much of the size, complexity and accordingly cost required for such equipment is accounted for by the rotating knives and attendant support structure generally utilized in such systems. It would accordingly be desirable if pellets of this type could be produced without the need of cutting knives. Such equipment without such conventional knives would be less expensive and more flexible in operation.
Although applicant is not aware of specific attempts to eliminate knife structures altogether, an attempt to eliminate more conventional knives as by the replacement thereof by a rotary cutoff device is shown in U.S. Pat. 3,003,193 issued Oct. 10, 1961. Therein thermoplastic polymer material is extruded along an extrusion barrel 11 and into a plurality of circumferentially spaced inwardly directed slots 20 positioned about the periphery of a die cutter boby 18. The interior portions of the die cutter body 18 are hollow and the unit is adapted to revolve by action of the screw against a discharge member 10 positioned at the exit end of the die. Coolant is introduced to the interior portions of the die cutter 18 by means of a channel 26, passes into an annular groove 24 and then outwardly into grooves or slots 23 spaced between and radially overlapping the slots 20. The discharge member 10 also includes outlet 25 and upon rotation of the die cutter 18 material passes from the slots 20 intermittently into the outlets 25; the relative rotation between the die cutter body 18 and the discharge member 10 serving to cut or pelletize such material. The resultant pellets are thereafter cooled by the sequential admission of coolant from grooves 23. Thus the sequential and intermittent alignment of the grooves 20,23 with the discharge openings 25 eliminates the need for conventional cutoff device in the formation of the pellets. It is not known whether the eqipment or process disclosed in this patent was ever commercially utilized.
Attention is also directed to a recently introduced unique in die strand-quenching process disclosed in U.S. Pat. No. 3,981,959 issued Sept. 21, 1976. In such patent a system which permits drastically increased pelleting operation efficiencies by means of the introduction of a liquid coolant under pressure into direct contact with the outer surface of polymeric or other materials passing through it is disclosed. As the coolant enters the die orifice, a portion thereof is immediately vaporized to form at least a solidified outer wall of the material surrounding an inner core thereof. The wall of the orifice is simultaneously lubricated by non-vaporizing coolant to facilitate the passage of the material therethrough. Such system also contemplates, although not necessarily so, the subsequent cutting of the resultant strands into discrete material lengths or pellets by knives mounted for rotation with respect to the exit face of the die.
The above cited U.S. Patents and their discussion constitutes Applicant's Prior Art Statement, and in that regard a copy of such patents is filed simultaneously with this application.